Specifying size of Entry and Text widgets

["Robert A. Knop Jr." <rknop lilys lbl gov>]

I haven't been able to figure this out from the documentation, so
apologies if this is a stupid question.

Is there a way to specify the on-screen size of Entry and Text widget, in
units of character widths (or "nominal" character widths for a
proportional font) and lines?  The "set_usize" function for the Widget
class appears to operate in pixels, which isn't the most natural unit for
Entry and Text widgets, and is indeed a bad unit to use if you want a
modicum of font sensitivity.

-Rob